U.S. patent application number 11/131835 was filed with the patent office on 2006-11-23 for memory module system and method.
This patent application is currently assigned to Staktek Group L.P.. Invention is credited to James W. Cady, Paul Goodwin, Russell Rapport.
Application Number | 20060261449 11/131835 |
Document ID | / |
Family ID | 37431714 |
Filed Date | 2006-11-23 |
United States Patent
Application |
20060261449 |
Kind Code |
A1 |
Rapport; Russell ; et
al. |
November 23, 2006 |
Memory module system and method
Abstract
A circuit module is provided in which two secondary substrates
or cards or the rigid portions of a rigid flex assembly are
populated with integrated circuits (ICs). The secondary substrates
are connected with flexible circuitry. One side of the flexible
circuitry exhibits contacts adapted for connection to an edge
connector. The flexible circuitry is wrapped about an edge of a
preferably metallic substrate to dispose one of the two secondary
substrates on a first side of the substrate and the other of the
secondary substrates on the second side of the substrate.
Inventors: |
Rapport; Russell; (Austin,
TX) ; Goodwin; Paul; (Austin, TX) ; Cady;
James W.; (Austin, TX) |
Correspondence
Address: |
J. SCOTT DENKO
ANDREWS & KURTH LLP
111 CONGRESS AVE., SUITE 1700
AUSTIN
TX
78701
US
|
Assignee: |
Staktek Group L.P.
|
Family ID: |
37431714 |
Appl. No.: |
11/131835 |
Filed: |
May 18, 2005 |
Current U.S.
Class: |
257/666 |
Current CPC
Class: |
H01L 2924/0002 20130101;
H01L 2924/00 20130101; H01L 2924/0002 20130101; H05K 2201/1056
20130101; H05K 2201/10189 20130101; H05K 2201/09445 20130101; H05K
2201/056 20130101; H05K 2203/1572 20130101; G11C 5/04 20130101;
H05K 1/117 20130101; H05K 2201/10734 20130101; H05K 1/141 20130101;
H05K 3/0061 20130101; H05K 3/4691 20130101; H05K 2201/10159
20130101; H05K 1/189 20130101; H05K 1/147 20130101 |
Class at
Publication: |
257/666 |
International
Class: |
H01L 23/495 20060101
H01L023/495 |
Claims
1. A memory module comprising: a rigid primary substrate having
first and second opposing lateral sides and an edge; first and
second secondary substrates, the first secondary substrate being
populated with a first group of CSPs and disposed proximal to the
first lateral side of the rigid primary substrate and the second
secondary substrate being populated with a second group of CSPs and
disposed proximal to the second lateral side of the rigid primary
substrate; a first flex edge connector connected to the first group
of CSPs and a second flex edge connector connected to the second
group of CSPs; and a flexible circuit having a set of card edge
connector module contacts and first and second groups of flex edge
contacts, the first group of flex edge contacts being mated with
the first flex edge connector and the second group of flex edge
contacts being mated with second flex edge connector and the
flexible circuit being disposed about the edge of the rigid primary
substrate.
2. The memory module of claim 1 in which the first secondary
substrate is populated with at least one CSP that is not a memory
circuit and not within the first group of CSPs.
3. The memory module of claim 2 in which the second secondary
substrate is populated with at least one CSP that is not a memory
circuit and not within the second group of CSPs.
4. The memory module of claim 1 in which the first and second flex
edge connectors are mounted on the first and second secondary
substrates, respectively.
5. The memory module of claim 1 in which the first and second flex
edge connectors are mounted on the rigid primary substrate.
6. The memory module of claim 1 in which the rigid primary
substrate is comprised of a metallic material.
7. The memory module of claim 1 inserted into a card edge
connector.
8. A motherboard in a computer upon which motherboard is connected
the memory module of claim 7.
9. A memory module comprising: a rigid primary substrate having
first and second opposing lateral sides and an edge; a rigid flex
assembly having first and second rigid portions and a flexible
portion, the rigid first portion being populated with a first group
of CSPs and disposed proximal to the first lateral side of the
rigid primary substrate, the second rigid portion being populated
with a second group of CSPs and disposed proximal to the second
lateral side of the rigid primary substrate; the flexible portion
of the rigid flex assembly being disposed about the edge of the
rigid primary substrate; and a set of card edge connector module
contacts supported by the rigid primary substrate and connected to
the first and second groups of CSPs.
10. The memory module of claim 9 in which the rigid primary
substrate is comprised of metallic material.
11. The memory module of claim 9 in which the rigid flex assembly
is populated with at least one CSP having a second function in
addition to the first group of CSPs which are CSPs having a first
function.
12. The memory module of claim 9 inserted into a card edge
connector.
13. A motherboard in a computer upon which motherboard is connected
the memory module of claim 12.
14. A circuit module comprising: a primary substrate having an edge
and first and second lateral sides; first and second secondary
substrates, each of which is populated with plural first CSPs each
having a first primary function, the first secondary substrate
being affixed to the primary substrate through adhesion of at least
one of the plural first CSPs to the primary substrate and the
second secondary substrate being affixed to the primary substrate
through adhesion of at least another one of the plural first CSPs
to the primary substrate; and a flexible circuit connected to the
plural first CSPs on the first secondary substrate through a flex
edge connector and the flexible circuit being disposed about the
edge of the substrate.
15. The circuit module of claim 14 in which the adhesion is
effectuated with thermally conductive adhesive.
16. The circuit module of claim 14 inserted into a card edge
connector.
17. A motherboard in a computer upon which motherboard the circuit
module of claim 16 is connected.
18. The circuit module of claim 14 in which the plural first CSPs
are single die memory circuits.
19. The memory module of claim 14 in which the primary substrate is
comprised of a metallic material.
20. The memory module of claim 14 in which the plural first CSPs
populating the secondary substrates are arranged in dual ranks on
each of the respective sides of the secondary substrates.
21. The memory module of claim 14 in which the first secondary
substrate is populated with at least one second CSP having a second
primary function.
22. The memory module of claim 21 in which the second primary
function is signal buffering.
23. The memory module of claim 21 in which the second primary
function is graphics processing.
24. A circuit module comprising: a substrate having an edge and
first and second lateral sides, the substrate being comprised of a
first portion and a second portion; and first and second secondary
substrates, the first secondary substrate being disposed adjacent
to the first lateral side of the substrate and the second secondary
substrate being disposed adjacent to the second lateral side of the
substrate; a flex circuit having two rows of multiple card edge
connector contacts symmetrically arranged about a midline of the
flex circuit, the flex circuit additionally having first and second
sets of flex edge contacts devised to mate with flex edge
connectors, the flex circuit being disposed about the edge of the
substrate to dispose a first one of the two rows of multiple card
edge connector contacts adjacent to the first lateral side of the
substrate and a second one of the two rows of multiple card edge
connector contacts adjacent to the second lateral side of the
substrate.
25. The circuit module of claim 24 in which the first portion of
the substrate is FR4 and the second portion of the substrate is
comprised substantially of metal.
Description
FIELD
[0001] The present invention relates to systems and methods for
creating high density circuit modules.
BACKGROUND
[0002] The well-known DIMM (Dual In-line Memory Module) board has
been used for years, in various forms, to provide memory expansion.
A typical DIMM includes a conventional PCB (printed circuit board)
with memory devices and supporting digital logic devices mounted on
both sides. The DIMM is typically mounted in the host computer
system by inserting a contact-bearing interface edge of the DIMM
into an edge connector socket. Systems that employ DIMMs provide
limited space for such devices and conventional DIMM-based
solutions have typically provided only a moderate amount of memory
expansion.
[0003] As die sizes increase, the limited surface area available on
conventional DIMMs limits the number of devices that may be carried
on a memory expansion module devised according to conventional DIMM
techniques. Further, as bus speeds have increased, fewer devices
per channel can be reliably addressed with a DIMM-based solution.
For example, 288 ICs or devices per channel may be addressed using
the SDRAM-100 bus protocol with an unbuffered DIMM. Using the
DDR-200 bus protocol, approximately 144 devices may be addressed
per channel. With the DDR2-400 bus protocol, only 72 devices per
channel may be addressed. This constraint has led to the
development of the fully-buffered DIMM (FB-DIMM) with buffered C/A
and data in which 288 devices per channel may be addressed. With
the FB-DIMM, not only has capacity increased, pin count has
declined to approximately 69 signal pins from the approximately 240
pins previously required.
[0004] The FB-DIMM circuit solution is expected to offer practical
motherboard memory capacities of up to about 192 gigabytes with six
channels and eight DIMMs per channel and two ranks per DIMM using
one gigabit DRAMs. This solution should also be adaptable to next
generation technologies and should exhibit significant downward
compatibility.
[0005] This improvement has, however, come with some cost and will
eventually be self-limiting. The basic principle of systems that
employ FB-DIMM relies upon a point-to-point or serial addressing
scheme rather than the parallel multi-drop interface that dictates
non-buffered DIMM addressing. That is, one DIMM is in
point-to-point relationship with the memory controller and each
DIMM is in point-to-point relationship with adjacent DIMMs.
Consequently, as bus speeds increase, the number of DIMMs on a bus
will decline as the discontinuities caused by the chain of
point-to-point connections from the controller to the "last" DIMM
become magnified in effect as speeds increase.
[0006] A variety of techniques and systems for enhancing the
capacity of DIMMs and similar modules are known. For example,
multiple die may be packaged in a single IC package. A DIMM module
may then be populated with such multi-die devices. However,
multi-die fabrication and testing is complicated and few memory and
other circuit designs are available in multi-die packages.
[0007] Others have used daughter cards to increase the capacity of
DIMMs but better construction strategies and reduced component
counts would improve such modules and their cost of production.
More efficient methods to increase the capacity of a DIMM, whether
fully-buffered or not, find value in computing systems.
SUMMARY
[0008] A circuit module is provided in which two secondary
substrates or cards or a rigid flex assembly are populated with
integrated circuits (ICs). The secondary substrates or rigid
portions of the rigid flex assembly are connected with flexible
portions of flex circuitry. One side of the flex circuitry exhibits
contacts adapted for connection to an edge connector. The flex
circuitry is wrapped about an edge of a preferably metallic
substrate to dispose one of the two secondary substrates on a first
side of the substrate and the other of the secondary substrates on
the second side of the substrate.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is a depiction of a module devised in accordance with
a preferred embodiment of the present invention.
[0010] FIG. 2 depicts a secondary substrate as may be employed in a
preferred embodiment of the present invention.
[0011] FIG. 3 depicts a first side of a flex circuit devised in
accordance with a preferred embodiment of the present
invention.
[0012] FIG. 4 depicts a cross-sectional view of a module devised in
accordance with a preferred embodiment of the present
invention.
[0013] FIG. 5 is a close up depiction of the area of FIG. 4
identified by A.
[0014] FIG. 6 is a magnified depiction of the area of FIG. 4
identified by B.
[0015] FIG. 7 is an exploded cross section of a flex circuit
employed in an alternate preferred embodiment of the present
invention.
[0016] FIG. 8 is another embodiment of the present invention.
[0017] FIG. 9 depicts yet another embodiment of the present
invention.
[0018] FIG. 10 depicts a module in accordance with an embodiment of
the present invention.
[0019] FIG. 11 is an enlarged depiction of an example connector
employed in an alternative embodiment of the present invention.
[0020] FIG. 12 depicts yet another embodiment having a two part
substrate.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0021] FIG. 1 depicts module 10 devised in accordance with a
preferred embodiment of the present invention. On each side of
primary substrate 14 are disposed a secondary substrate 21 on which
reside ICs 18 which are, in the depicted embodiment, chip-scale
packaged memory devices. A portion of flex circuit 12 is shown
along lower edge of primary substrate 14. Expansion or edge
connector module contacts 20 are disposed along side 8 of flex
circuit 12 and, in preferred embodiments, some expansion or edge
connector module contacts 20 will be exhibited on each of the two
sides of module 10 although in some embodiments, the edge connector
or module contacts 20 may be present on only one side of module 10.
Primary substrate 14 may be PCB material or F4 board, for example,
or, in preferred embodiments, it will be a metallic material such
as, for example, a metallic alloy or mixture, or copper or
aluminum, for example, to allow more effective thermal
management.
[0022] For purposes of this disclosure, the term chip-scale or
"CSP" shall refer to integrated circuitry of any function with an
array package providing connection to one or more die through
contacts (often embodied as "bumps" or "balls" for example)
distributed across a major surface of the package or die. CSP does
not refer to leaded devices that provide connection to an
integrated circuit within the package through leads emergent from
at least one side of the periphery of the package such as, for
example, a TSOP.
[0023] Embodiments of the present invention may be employed with
leaded or CSP devices or other devices in both packaged and
unpackaged forms but where the term CSP is used, the above
definition for CSP should be adopted. Consequently, although CSP
excludes leaded devices, references to CSP are to be broadly
construed to include the large variety of array devices (and not to
be limited to memory only) and whether die-sized or other size such
as BGA and micro BGA as well as flip-chip. As those of skill will
understand after appreciating this disclosure, some embodiments of
the present invention may be devised to employ stacks of ICs each
disposed where an IC 18 is indicated in the exemplar Figs.
[0024] Multiple integrated circuit die may be included in a package
depicted as a single IC 18. In this embodiment, memory ICs are used
in accordance with the invention to provide a memory expansion
board or module. Various other embodiments may, however, employ a
variety of integrated circuits and other components. Such variety
may include microprocessors, FPGA's, RF transceiver circuitry, and
digital logic, as a list of non-limiting examples, or other
circuits or systems which may benefit from enhanced high-density
circuit board or module capability. Thus, the depicted multiple
instances of IC 18 may be devices of a first primary function or
type such as, for example, memory, while other devices such as
depicted circuit 19 may be devices of a second primary function or
type such as, for example, signal buffers, one example of which is
the Advanced Memory Buffer ("AMB") in the fully-buffered circuitry
design for modules. IC 19 may also be, for example, a thermal
sensor that generates one or more signals which may be employed in
determinations of the heat accumulation or temperature of module
10. Integrated circuit 19 may also be, for example, a graphics
processor for graphics processing. When circuit 19 is a thermal
sensor, it may mounted on the inner face of secondary substrate 21
relative to primary substrate 14 of module 10 to more accurately be
able to sense the thermal condition of module 10. Circuit 19
depicted on FIGS. 1 and 2 should be understood to not have been
depicted to accurate scale but merely as an exemplar.
[0025] FIG. 2 depicts an exemplar secondary substrate 21 populated
with a group of ICs 18 of a first primary function. As will be
illustrated, several embodiments may be devised that will exhibit
first and second secondary substrates each populated with a group
of CSPs. Secondary substrate 21 may be composed from a variety of
materials and, typically, will be comprised from a PCB material
although other materials known in the art may be employed as
secondary substrates in accordance with the invention. For example,
secondary substrate 21 may be provided by the rigid portion of an
integrated rigid flex structure that provides mounting fields for
ICs 18, ICs 19, and other circuitry such as registers and PLLs, for
example, and a flexible portion that transits about primary
substrate 14 or extends to flex edge connectors mounted on primary
substrate 14. When secondary substrate 21 is discrete from, but
connected to, flex circuit 12, the connective network amongst ICs
18, IC 19 and other support circuitry is electrically accessible on
flex edge connectors 23 such as those depicted in FIG. 2, for
example. Secondary substrates 21 may exhibit single rank
dispositions of ICs 18 or may, in alternative embodiments, exhibit
more than one rank of ICs on one or both sides.
[0026] FIG. 3 depicts side 8 of a preferred flex circuit 12
("flex", "flex circuitry", "flexible circuit", "flexible
circuitry") used in constructing a module according to a preferred
embodiment of the present invention. The flexible circuitry
maintains a substantially continuous and controlled impedance
circuit across the flexible circuit. This is in contrast to prior
art techniques that provide a circuit that travels from card edge
connector pads through a rigid PCB to a via or surface mount pad
for ICs. This results in an impedance discontinuity when the signal
passes through a wire or bus bar as part of a connector in the
circuit.
[0027] Flex circuit 12 is preferably made from one or more
conductive layers supported by one or more flexible substrate
layers as described with further detail in FIG. 7 herein. The
entirety of the flex circuit 12 may be flexible or, as those of
skill in the art will recognize, the flexible circuit 12 may be
made flexible in certain areas to allow conformability to required
shapes or bends, and rigid in other areas to provide the planar
mounting surfaces of secondary substrate 21. In such cases where
rigid-flex is employed, it should be considered as including
secondary substrates and flex circuitry and will be identified
herein in FIG. 8 as a single reference that combines both flex
circuitry and secondary substrate.
[0028] FIG. 3 depicts a first or outer side 8 of flex circuit 12.
Between a line "L", flex circuit 12 has two rows (CR1 and CR2) of
module contacts 20. Line L is, but need not be along the median
line of flex circuit 12. Contacts 20 are adapted for insertion in a
circuit board socket such as, in a preferred embodiment, an edge
connector. When flex circuit 12 is folded about edge 16A of primary
substrate 14, side 8 depicted in FIG. 1 is presented at the outside
of module 10. The opposing side of flex circuit 12 is on the inside
in the folded configuration of FIG. 4, for example. It is not
shown, but those of skill will be able to understand the dual-sided
nature of flex circuitry 12 without literal depiction of the other
side of flex circuit 12. The other or "second side" of flex circuit
12 is on the inside in several depicted configurations of module 10
and thus the second side of flex circuit 12 is closer to substrate
14 about which flex circuit 12 is disposed than is side 8. Other
embodiments may have other numbers of contacts arranged in one or
more rows or otherwise and there may be only one such row of
contacts and it may be on one side of line L rather than being
distributed on both sides of L or near an edge of the flex. Flex
edge contacts 25 are shown with flex circuit 12 in FIG. 3 and, in
the depicted embodiment, those flex edge contacts marked 25A
connect with a first secondary substrate 21A and that secondary
substrate's resident circuitry (such as ICs 18 and 19) through flex
edge connectors 23A while those referenced with 25B connect with a
second secondary substrate 21B through flex edge connectors 23B.
This embodiment arrangement is further illustrated in FIG. 4.
[0029] Other embodiments may employ flex circuits 12 that are not
rectangular in shape and may be square in which case the perimeter
edges would be of equal size or other convenient shape to adapt to
manufacturing or specification particulars for the application at
issue.
[0030] FIG. 4 is a cross section view of a module 10 devised in
accordance with a preferred embodiment of the present invention.
Module 10 is populated with ICs 18 having top surfaces 18.sub.T and
bottom surfaces 18.sub.B. Substrate or support structure 14 has
first and second perimeter edges 16A and 16B appearing in the
depiction of FIG. 4 as ends. Substrate or support structure 14
typically has first and second lateral sides S.sub.1 and S.sub.2.
Flex 12 is wrapped about or passed about perimeter edge 16A of
substrate 14 which, in the depicted embodiment, provides the basic
shape of a common DIMM form factor such as that defined by JEDEC
standard MO-256. That places a first part (121) of flex circuit 12
proximal to side S.sub.1 of substrate 14 and a second part (122) of
flex circuit 12 proximal to side S.sub.2 of substrate 14.
[0031] The depicted module 10 exhibits first secondary substrate
21A and second secondary substrate 21B, each of which secondary
substrates is populated with plural ICs 18 on each of their
respective sides 27 and 29 with sides 27 being inner with respect
to module 10. While in this embodiment, the four depicted ICs are
attached to respective secondary substrates in opposing pairs, this
is not limiting and more ICs may be connected in other arrangements
such as, for example, staggered or offset arrangements. Adhesive 31
shown partially in FIG. 4 may be employed to improve thermal energy
transfer to substrate 14 which is preferably a metallic or other
thermally conductive material. The module contacts 20 of flex
circuit 12 are illustrated in FIG. 4 as are flex edge connectors
23A and 23B.
[0032] Flex circuit 12 module contacts 20 are positioned in a
manner devised to fit in a circuit board card edge connector or
socket such as edge connector 33 mounted on mother board 35 shown
in FIG. 4 and connect to corresponding contacts in the connector
(not shown). Edge connector 33 may be a part of a variety of other
devices such as general purpose computers and notebooks. The
depicted substrate 14 and flex 12 may vary in thickness and are not
drawn to scale to simplify the drawing. The depicted substrate 14
has a thickness such that when assembled with the flex 12 and
adhesive employed to affix flex circuit 12 to substrate 14, the
thickness measured between module contacts 20 falls in the range
specified for the mating connector 33. In some other embodiments,
flex circuit 12 may be wrapped about perimeter edge 16B as those of
skill will recognize.
[0033] FIG. 5 illustrates an enlarged portion of an exemplar module
10. While module contacts 20 are shown protruding from the surface
of flex circuit 12 which transits about edge 16A of primary
substrate 14. This is not limiting, however, and other embodiments
may have flush contacts or contacts below the surface level of flex
12. Primary substrate 14 supports module contacts 20 from behind
flex circuit 12 in a manner devised to provide the mechanical form
required for insertion into a socket. While the depicted substrate
14 has uniform thickness, this is not limiting and in other
embodiments the thickness or surface of substrate 14 may vary in a
variety of ways to provide for a thinner module, for example.
[0034] In the vicinity of perimeter edge 16A or the vicinity of
perimeter edge 16B, the shape of substrate 14 may also differ from
a uniform taper. Substrate 14 in the depicted embodiment is
preferably made of a metal such as aluminum or copper, as
non-limiting examples, or where thermal management is less of an
issue, materials such as FR4 (flame retardant type 4) epoxy
laminate, PTFE (poly-tetra-fluoro-ethylene) or plastic. In another
embodiment, advantageous features from multiple technologies may be
combined with use of FR4 having a layer of copper on both sides to
provide a substrate 14 devised from familiar materials which may
provide heat conduction or a ground plane. Substrate 14 may also
exhibit an extension at edge 16B to assist in thermal
management.
[0035] One advantageous methodology for efficiently assembling a
circuit module 10 such as described and depicted herein is as
follows. First and second secondary substrates 21 that include flex
edge connectors 23 are populated on respective secondary substrate
sides 27 and 29 with circuitry such as ICs 18. Flex circuitry 12 is
brought about primary substrate 14 and secondary substrates 21A and
21B are attached to primary substrate 14 through adhesion of upper
side 18T of inner ICs 18 to primary substrate 14 and flex edge
contacts 25 are mated with respective flex edge connectors 23.
[0036] FIG. 6 depicts in enlarged detail a portion of an exemplar
module 10 illustrating the inclusion of two ranks of ICs 18 on each
of two sides of module 10. First and second secondary substrates
21A and 21B are depicted as populated with ICs 18 on each of their
respective sides 27 and 29. This enlarged view illustrates CSP
contacts 37 of ICs 18. Flex edge connectors 23A and 23B are shown
mated with flex edge contacts 25A and 25B, respectively. Those of
skill will note that, although unwieldy, in some alternative
modules 10, flexible circuitry may also transit over top edge 16B
of substrate 14 to reduce signal density in flex circuit 12 that
transits about edge 16A.
[0037] FIG. 7 is an exploded depiction of a flex circuit 12
cross-section according to one embodiment of the present invention.
The depicted flex circuit 12 has four conductive layers 701-704 and
seven insulative layers 705-711. The numbers of layers described
are merely those used in one preferred embodiment and other numbers
of layers and arrangements of layers may be employed. Even a single
conductive layer flex circuit 12 may be employed in some
embodiments, but flex circuits with more than one conductive layer
prove to be more adaptable to more complex embodiments of the
invention.
[0038] Top conductive layer 701 and the other conductive layers are
preferably made of a conductive metal such as, for example, copper
or alloy 110. In this arrangement, conductive layers 701, 702, and
704 express signal traces 712 that make various connections by use
of flex circuit 12. These layers may also express conductive planes
for ground, power or reference voltages.
[0039] In this embodiment, inner conductive layer 702 expresses
traces connecting to and among various devices mounted on the
secondary substrates 21. The function of any one of the depicted
conductive layers may be interchanged in function with others of
the conductive layers. Inner conductive layer 703 expresses a
ground plane, which may be split to provide VDD return for
pre-register address signals. Inner conductive layer 703 may
further express other planes and traces. In this embodiment, floods
or planes at bottom conductive layer 704 provides VREF and ground
in addition to the depicted traces.
[0040] Insulative layers 705 and 711 are, in this embodiment,
dielectric solder mask layers which may be deposited on the
adjacent conductive layers for example. Other embodiments may not
have such adhesive dielectric layers. Insulating layers 706, 708,
and 710 are preferably flexible dielectric substrate layers made of
polyimide. However, any suitable flexible circuitry may be employed
in the present invention and the depiction of FIG. 7 should be
understood to be merely exemplary of one of the more complex
flexible circuit structures that may be employed as flex circuit
12.
[0041] FIG. 8 depicts an embodiment in accordance with the present
invention. In the depicted embodiment of FIG. 8, secondary
substrates 21A and 21B are a part of rigid flex assembly 12RF. Flex
assembly 12RF includes secondary substrate portions 21A and 21B and
corresponding flexible portions 12FA and 12FB which, although
preferably of one piece, are separately identified to show the
first and second flexible portions of the flex assembly that are
most proximal to sides S1 and S2 of substrate 14, respectively. As
depicted, preferably, flexible portions 12FA and 12FB are of one
piece as flex assembly 12RF is brought about edge 16A of substrate
14. As those of skill will recognize, use of a single flex assembly
has manufacturing advantages in that, amongst other things, a
single flex circuit is handled through assembly rather than two
pieces.
[0042] FIG. 9 depicts another embodiment in accordance with the
present invention. Module 10 as depicted in FIG. 9 employs a flex
circuit 12 identified as being of two portions 12A and 12B that are
attached to respective first and second secondary substrates 21A
and 21B by soldering of flex edge pads to the secondary substrates
as indicated at the area denoted with an "S". Flex circuit 12
transits about edge 16A of substrate 14. As shown in the depiction
of FIG. 9, extension 16T from substrate 14 increases the mass and
radiative surface area of substrate 14 thus giving module 10
greater opportunity to reduce accumulation of thermal energy.
[0043] FIG. 10 depicts another embodiment in accordance with the
present invention. In module 10 as depicted in FIG. 10, secondary
substrates 21 are connected to module contacts 20 of primary
substrate 14 with connectors 40.
[0044] FIG. 11 is an enlarged depiction of the area around
connector 40B on side S2 of primary substrate 14 in the embodiment
depicted in FIG. 10. Depicted connector 40B has first parts 401 and
second parts 402 that mate and provide controlled impedance paths
for signals. Connectors such as connector 40 are available in a
variety of types and configurations and one example provider of
such connectors is Molex.
[0045] FIG. 12 depicts an alternative embodiment of module 10 in
accordance with the present invention. As depicted in FIG. 12,
conductive pins 42 are employed to connect secondary substrates 21
to a portion of primary substrate 14 identified as 14B. In the
depiction, substrate 14 is delineated into portions 14A and 14B
that are joined at area "C". Techniques for joining two portions of
dissimilar materials are known in the art and the proposed
alternative shown is a tounge and groove arrangement between
portion 14A and 14B at area C but those of skill will recognize
after appreciating this specification that any of a number of
techniques may be employed to join portions 14A and 14B into a
substrate 14. Portion 14B is comprised of a board such as FR4 and
includes conductive traces or areas that are employed to connect
the conductive pins 42 to contacts 20 that are, preferably, devised
for insertion in an edge connector. Portion 14A of substrate 14 is
comprised of metal such as, for example, aluminum or copper or
copper alloy. Module 10 is shown with extension 16T that increases
the thermal performance of module 10, particularly in embodiments
where portion 14A is metal.
[0046] The present invention may be employed to advantage in a
variety of applications and environment such as, for example, in
computers such as servers and notebook computers by being placed in
motherboard expansion slots to provide enhanced memory capacity
while utilizing fewer sockets. Two high rank embodiments or single
rank embodiments may both be employed to such advantage as those of
skill will recognize after appreciating this specification.
[0047] Although the present invention has been described in detail,
it will be apparent to those skilled in the art that many
embodiments taking a variety of specific forms and reflecting
changes, substitutions and alterations can be made without
departing from the spirit and scope of the invention. Therefore,
the described embodiments illustrate but do not restrict the scope
of the claims.
* * * * *